Flat panel field emission displays (FEDs), like standard cathode ray tube (CRT) displays, generate light by impinging high energy electrons on a picture element (pixel) of a phosphor screen. The excited phosphor then converts the electron energy into visible light. However, unlike conventional CRT displays which use a single or in some cases three electron beams to scan across the phosphor screen in a raster pattern, FEDs use stationary electron beams for each color element of each pixel. This allows the distance from the electron source to the screen to be very small compared to the distance required for the scanning electron beams of the conventional CRTs. In addition, the vacuum tube of the FED can be made of glass much thinner than that of conventional CRTs. Moreover, FEDs consume far less power than CRTs. These factors make FEDs ideal for portable electronic products such as laptop computers, pocket-TVs and portable electronic games.
As mentioned, FEDs and conventional CRT displays differ in the way the image is produced. Conventional CRT displays generate images by scanning an electron beam across the phosphor screen in a raster pattern. As the electron beam scans along the row (horizontal) direction, its intensity is adjusted according to the desired brightness of each pixel of the row. After a row of pixel is scanned, the electron beam steps down and scans the next row with its intensity modulated according to the desired brightness of that row. In contrast, FEDs generate images according to a "matrix" addressing scheme. Each electron beam of the FED is formed at the intersection of individual rows and columns of the display. Rows are updated sequentially. A single row electrode is activated with all the columns active, and the voltage applied to each column determines the magnitude of the electron beam formed at the intersection of that row and column. Then, the next row is subsequently activated and new brightness information is set again on each of the columns. When all the rows have been thus updated, a new frame has been displayed.
When the columns of a FED are driven with rapidly changing voltage levels, they can be viewed as electrically equivalent to transmission lines. This is due to the fact that a column line is itself a network of distributed resistance and capacitance. Thus, as a signal is propagated down the column line, the signal may degrade and the voltage potential of the signal may drop, making the driven end slightly brighter than the non-driven end of the column line. In a single-end driven display where column drivers are disposed across the top portion of the display, the resultant effect can be a gradual reduction in brightness from the top to bottom of the display. In an interdigitated display where interleaving column lines are driven on opposite ends of the display (e.g., top, bottom, top, bottom, etc.), the resultant effect can be a "comb-like" pattern (or, alternating bright and dark bands) along the top and bottom edges of the display. Although these visual artifacts are hardly noticeable in small and low resolution displays, they can be glaring in larger and higher resolution displays.
One method of eliminating such "transmission line" effects is by varying the resistance of the column traces along their length. For example, the width of the column traces can be made to be wider (thus less resistive per unit length) at the far end and narrower (thus more resistive per unit length) at the driven end. That method, however, is disadvantageous because column traces with a "tapered" width are difficult and expensive to manufacture.
Therefore, what is needed is a field emission display that does not exhibit brightness degradation along the column lines. What is further needed is a system and method for eliminating visual artifacts caused by signal deterioration along the column traces due to transmission line effects. What is yet further needed is a system and method for eliminating such visual artifacts without compromising the gray-scale resolution of the display.